Manufacture of bifocal lenses.



PATENT orrion.

JAMES AITCHISON, OFYALONDON, ENGLAND,

rr/rnrmfrnofrURE lor BIFOCAL LENsEs.

To all whom 'it may con-cem.'

Be it known that I, JAMES ITCHISON, a subject of the King of GreatA Britain, residing at llt Newgate street, in the city of London, England, have invented certain newfand useful Improvements in the Manufacture of Bifocal Lenses, of which the following is a specification.

This invention relates to that description of bifocal lens for spectacles and the like in which the minor lens is made from glass of higher refractive indexand is contained within vthe glassof the major lens so that no edges or joints of the lens are presenton -either face of the bifocal lens, the-major lens being made of two pieces of glass which completely inclosethe glass minor lens. In the manufacture of Asuch lenses there is considerable difliculty experienced and much time is occupied in grinding and fit-ting the glass minor lens, the cost of'such bifocal lenses being nearly prohibitive.

Hy invention has for its object improvements in such lenses and in the manufacture thereof whereby the cost of production is largely decreased while retaining the necessary accuracy and efficiency.

According to my invention, I fill the recess, which Ais formed to the desired curvature of the minor lens in one glass of the major lens, with a suitable colorless cement such as balsam having a higher refractive index than the glass of the major lens; the other glass of the major lens is placed over the recessed face of that glass of the major lens so as to completely inclose the balsam, and the whole is allowed to set.` The glass of the major lens may be given the desired curvature before or subsequent to the cenicnting together'.

In the acconilianying drawings, Figure l illustrates diagrannnatically my invention with regard to plane (parallel) glasses and Fig. 2 to periscopic glasses.

The glasses of which the major lens is composed are commonly of twodi'flierent, thicknesses, the thicker glass L being formed with -the,Nregesslm forwthe minor lens. The surface of the glass a is according to my invention, flooded with a high quality, coloilcss,ccment suchas Balsam inv meltedstate, filling the recess fr, as indiw cated byv the Vdotted lines; the cover glass c 1s then placed in position upon the recessed glass a in the ordinary manner, and the biv Specification of Letters Patent. Application 1aed January 17, 190s.

Patented May- 30, 1911.

serial N o. 411,373.

focallens so produced is subjected to' a baki ing heat for a time and then allowed to set, the minor lens being then composed of solid balsam which has acquired greater hardness .through the more or less protracted baking.y

glasses of a major lens inclose aminor lens between them, consisting in providing one glass of the major lens with a recess shaped to conform to the shape of the desired minor lens, filling said recess with a colorless cement in a liquid state, placing the other glass of the major lens upon the raised snrface of the first named glass, and allowing the cementto harden.

2. A method of manufacturing bifocal lenses of the description in which the shaped glasses of a major lens inclose a minor lensl between them, consisting in providing one glass of the major lens with a recess shaped I to conform to the shape of the desired minor lens, filling said recess with a colorless cement in a liquid state, placing theotherglass of the major lens upon the raised surface of the first named glass, subjecting the combined glass to the action of heat, and allowing the cement to harden.

3; Method of manufacturing bifocal lenses of thc description in which the shaped glasses of a major lens inclose a minorf'jlns. between them, consisting in providing one glass of the major lens with a recess shaped to conform to the shape of the desired minor lens, fiooding the recessed surface of the said glass of the major lens with a colorless Canada balsam in a melted state, ap- .plying the other glass of the major lens to said flooded surface.; subjecting the combined glasses to a baking heat, and finally allowingr the whole to set, as set forth.

i 4. Method of manufacturing bifocal lenses of the description in which the shaped glasses of a major lens nclose a minor lens between them consisting in providing onegl'ass of the major lens with a recess sha. ed to conform to the shape of the desire 'minor lens, flooding the recessed surface of the said glass with a'colorless Canada, balsam in a melted state, applying the-other glass to said flooded surface; sub.- jecting the combined glasses to light pressure to express surplus fluid cement, sub- `ecting the combined glasses to a baking eat, and finally allowing the Whole to set, as set forth;

5. Method of manufacturing bifocal lenses consisting in forming the major lens of two pieces or suitable glass shaped to the desired curvature, forming a -re'eess conformin to the curvature of the desired minor ens in one of said glasses, flooding the recessed surface of said glass with a co1- orless Canada balsem in a melted state, applying the other glass to said flooded surface; Vsubjecting the combined glasses to a baking heat, and finally allowing the whole to'set as set forth.

6. Method cf manufacturing bifocal lenses, consisting in forming the major lexis of two pieces of suitable glass, formin a recess conforming to the curvature of tie desired minor lens in one of said glasses, Hooding the recessed surface of said glass with a colorless Canada balsam in a melted state, applying the other glass to said flooded surface; subjecting the combined glasses to a baking heat, and shaping the combined glasses'to the desired external curvature or curvatures after the whole has thoroughly set, as set forth. 4

In witness whereof I have hereunto set my hand in presence of two Witnesses.

JAMES AITCHISON.

lVitnesses:

GEORGE C. DOWNING, G. F. WARREN.

Copies ci this patent may be obtained yi'orr ve cents each, by addressing the Commissioner of Patents, Washington, D. C.- 

